Concentrating solar collector

ABSTRACT

A solar energy collector is provided having at least one reflector panel, a plurality of solar receivers, and a support structure that supports the at least one reflector panels in a manner that defines a reflector troughs having a trough base, a pair of reflective side walls and a trough aperture suitable for receiving incident sunlight during operation of the collector, wherein each reflective side wall has a curvature that approximates a quarter parabola segment to thereby concentrate incident solar radiation on the plurality of solar receivers.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.61/043,704 filed on Apr. 9, 2008, entitled “Dual Trough ConcentratingSolar Photovoltaic Module” and to U.S. Provisional Application No.60/970,007 filed on Sep. 5, 2007, entitled “Dual Trough ConcentratingPhotovoltaic Module”, both of which are incorporated by reference hereinfor all purposes.

FIELD OF THE INVENTION

The present disclosure relates generally to solar energy collectingsystems, and more particularly to concentrating solar energy collectingsystems.

BACKGROUND OF THE INVENTION

The highest cost components of a solar photovoltaic (PV) system are thesolar cells that convert sunlight to electricity by the photoelectriceffect. To use these cells more effectively, concentrating photovoltaic(CPV) systems focus sunlight from a larger aperture onto a smaller cellarea. Although many CPV designs have been developed from the verybeginning of the commercial PV industry in the 1960's, not one hasachieved significant commercial success as of late 2007. Although CPVdesigns use less active cell material, they typically require additionalstructure such as mirrors, lenses and heat sinks, and are fundamentallylimited to utilizing less then all of the total available light. Thesefactors increase cost and system complexity and reduce theoptical-to-electrical efficiency over non-concentrating PV systems.

Although existing concentrating solar PV systems address someapplications, there are continuing efforts to further improve the designand cost effectiveness of concentrating PV system.

SUMMARY

A solar energy collector is provided having at least one reflectorpanel, a plurality of solar receivers, and a support structure thatsupports the at least one reflector panels in a manner that defines areflector troughs having a trough base, a pair of reflective side wallsand a trough aperture suitable for receiving incident sunlight duringoperation of the collector, wherein each reflective side wall has acurvature that approximates a quarter parabola segment to therebyconcentrate incident solar radiation on the plurality of solarreceivers.

In another embodiment, a photovoltaic solar energy collector suitablefor use in a solar energy collection system that tracks movements of thesun along at least one axis having an aperture, at least one reflectorpanel, and at least one solar receiver, each solar receiver including aplurality of photovoltaic cells having cell faces that are orientedsubstantially perpendicular to the collector aperture.

In yet another embodiment, a photovoltaic solar energy collectorsuitable for use in a solar energy collection system that tracksmovements of the sun along at least one axis can have a trough stylereflector arrangement a trough base, a pair of reflective side walls, alongitudinal axis, a trough aperture suitable for receiving incidentsunlight during operation of the solar energy collection system, thetrough aperture having an aperture axis that is substantiallyperpendicular to the longitudinal axis, and a plurality of solarreceivers, each solar receiver being positioned generally adjacent andabove an associated side wall such that the solar receivers do not shadethe reflective side walls during operation in a mode the tracks movementof the sun along one axis. Each solar receiver has a base plate, and atleast one photovoltaic cell carried on a front surface of the baseplate.

A method for using a solar concentrating collector may compriseassembling one or more solar concentrating collectors, each solarconcentrating collector having at least one photovoltaic cell, andtracking the one or more solar concentrating collectors, wherein a facenormal of the photovoltaic cell is perpendicular to the incidentsunlight.

These and other features will be presented in more detail in thefollowing detailed description of the invention and the associatedfigures.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and constitute apart of this specification, illustrate one or more example embodimentsand, together with the description of example embodiments, serve toexplain the principles and implementations.

In the drawings:

FIGS. 1A-1F illustrate an exemplary dual trough concentratingphotovoltaic solar energy collector in accordance with one embodiment ofthe present invention.

FIGS. 2A and 2B illustrate an expanded perspective view of the exemplarysolar energy collector.

FIGS. 3A-3D illustrate detailed sections of the collector illustrated inFIG. 2B.

FIGS. 4A-4E illustrate exemplary embodiments of a solar receiver.

FIG. 5 illustrates an exemplary heat sink.

FIGS. 6A and 6B illustrate another exemplary heat sink.

FIGS. 7A-7C illustrate yet another exemplary heat sink.

FIG. 8 illustrates an exemplary attachment of a solar receiver to asupport structure.

FIGS. 9A-9C illustrate an exemplary shipping container for the solarenergy collectors.

FIGS. 10A-10D illustrate an exemplary power generation plant inaccordance with an embodiment of the invention that utilizes an array ofsolar energy collectors.

DESCRIPTION OF EXAMPLE EMBODIMENTS

Embodiments are described herein in the context of a dual troughconcentrating solar photovoltaic module. The following detaileddescription is illustrative only and is not intended to be in any waylimiting. Other embodiments will readily suggest themselves to suchskilled persons having the benefit of this disclosure. Reference willnow be made in detail to implementations as illustrated in theaccompanying drawings. The same reference indicators will be usedthroughout the drawings and the following detailed description to referto the same or like parts.

In the interest of clarity, not all of the routine features of theimplementations described herein are shown and described. It will, ofcourse, be appreciated that in the development of any such actualimplementation, numerous implementation-specific decisions must be madein order to achieve the developer's specific goals, such as compliancewith application- and business-related constraints, and that thesespecific goals will vary from one implementation to another and from onedeveloper to another. Moreover, it will be appreciated that such adevelopment effort might be complex and time-consuming, but wouldnevertheless be a routine undertaking of engineering for those ofordinary skill in the art having the benefit of this disclosure.

A solar energy collection system is described. FIGS. 1A-1C illustrate anexemplary dual trough solar energy concentrator or collector suitablefor use with various embodiments of the present invention. FIG. 1A is aperspective view of the dual trough solar energy collector, FIG. 1B is atop perspective view of the dual trough solar energy collector, FIG. 1Cis a side view of the dual trough solar energy collector, and FIG. 1D isa bottom view of the dual trough solar energy collector. The collector100 has a dual trough design with two optical apertures 101 a and 101 bsymmetrically situated about a bisecting plane 105 (FIG. 1C). Theoptical apertures 101 admit incident sunlight onto reflector panels 106.The support structure 102 is arranged to support at least four reflectorpanels 106. Reflector panels 106 are attached to the support structure102 forming a reflector structure 107 (FIG. 2A). The reflector structure107 may have a pair of adjacent reflector troughs 120 a, 120 b, eachtrough having a base 124 a, 124 b, and a pair of reflective side wallsformed from the reflector panels 106. Reflector structure 107 may beconfigured so as to direct incident sunlight entering collector 100through the optical apertures 101 toward a region slightly above a topedge of the opposing reflector panel 106. The support structure 102 iscomposed of a plurality of shaping ribs 216 (FIG. 2A) and othercomponents as further described in detail below. The collector 100 alsohas a plurality of receivers or solar receivers 104 coupled near the topedges of the reflector structure 107 as further described in detailbelow.

FIGS. 1E and 1F illustrate a cross-sectional diagram of the troughs.Each collector 100 has a longitudinal axis 162 (FIG. 1A) and each trough120 a, 120 b has an optical aperture 101 (FIG. 1E). For the purposes ofthis explanation, we utilize the term aperture to refer to the effectivetrough opening that exists when the collector is directly facing thesun. We also use the term normal axis 160 (or aperture axis or lateralaxis as illustrated in FIG. 1A) to refer to a geometric axis that isperpendicular to the longitudinal axis and parallel to incident solarradiation when the collector is facing directly towards the sun. If thetrough is symmetrical, the trough may also have a trough bisecting plane134 dividing the trough into two substantially symmetric halves, eachsubstantially symmetric half resembling a longitudinally extended curvedsection. In other embodiments, the trough halves may be asymmetrical.The reflectors that define the troughs are curved to direct sunlighttowards an associated solar receiver. The curvature of the troughs canvary somewhat. In one embodiment, each substantially symmetric half hasa curvature resembling that of a quarter section of a parabola 132. Inother words, the curvature of the troughs may approximate an arc of acircle or any other geometries that provide suitable concentration ofthe sunlight at the targeted receivers. In the quarter sectionembodiment, each trough 120 a, 120 b may be composed of two quartersection of a “full” or traditional parabola having the same focus.Although described as a quarter section of a parabola this descriptionis not intended to be limiting as the troughs 120 are approximatelysimilar to a quarter section of a parabola shape and not an exactlymathematically perfect parabola shape.

FIG. 1E illustrates a traditional center-focusing full parabolaconfiguration 130, with a focus at 135, superimposed and compared to theuse of two quarter sections of a parabola 132. As compared to the fullparabola configuration 130, use of a substantially quarter of a parabola132 configuration provides for a deeper or V-shaped trough and each sideof the trough has less curvature. A quarter section of a parabola 132 isa section of a parabola such that when two opposing quarter sections arepositioned adjacent to each other the focus of one section is near thetop edge of the opposing section. For example, the focus for section 132a is at 133 a and the focus for section 132 b is at 133 b. The quarterparabolic trough 132 achieves the same geometric concentration as a fullparabola concentrator, but has a lower curvature and may also bestiffer. The reduced curvature also reduces the stress in a bentreflector panel 106 and allows reflector panel 106 to be formed from agenerally planar panel. The increased stiffness results from the shapehaving a higher area moment of inertia. Having a deeper trough and/ortruss (as discussed below) also generally provides for a stiffercollector than a shallower one. Additionally, for a fixed axial load, astraighter beam may be stiffer than a curved beam. The increasedintrinsic stiffness of this design allows collector 100 to be fabricatedusing lighter and less expensive materials such as aluminum, sheetmetal, and the like.

Referring back to FIGS. 1A-1C, the support structure 102 may support orhold a plurality of reflector panels 106. The reflector panels 106 maybe shaped by elastic deformation against shaping ribs 216 (FIGS. 2A and2B) of the support structure 102. In one embodiment, the reflectorpanels 106 may be plastically formed with a curvature. Thus, thereflector panels 106 may be supported and held by the structure 102 witha curvature resembling a quarter parabolic configuration, as furtherdiscussed in detail below with reference to FIGS. 2A and 2B.

Although a single quarter parabolic trough provides higher bendingstiffness than the equivalent full parabolic trough, it is an open shapeand may thus have low torsional stiffness. Torsional stiffness isdesirable because the solar energy collector is rotated during the dayto align to the sun. To provide for additional torsional stiffness, theillustrated collector 100 has a stiffening frame 108 coupled to bottoms124 a and 124 b of the shaping ribs 216 or support frame 102. This formsa closed truss 136, as illustrated in FIG. 1C, in a region between thetroughs 120 a, 120 b below the reflector panels 106. The closedcollector support truss 136 framework forms a trapezoidal-shaped torquetube. Although described as a trapezoidal shape, the truss 136 isapproximately similar to a trapezoidal shape and not an exactlymathematically perfect trapezoidal shape. Given the large apertures 101and the light weight of the collector 100, the trapezoidal torque tubeprovides for a stiff structure.

As illustrated in FIG. 1F, the quarter parabola trough configuration orshape is configured to direct the focus of the troughs 120 to a locationjust above the far edge of the opposing trough segment. This allows thesolar receivers 104 to be located where they will not shade thereflector panels 106. Additionally, the solar receivers 104 may beattached to the trough 120 edges 103 without the use of struts thatextend over the faces of the reflector panels. Traditionally, a closedshaped truss is created by installing struts over the trough opening.The struts cast shadows over the reflector panels, which results in aless efficient photovoltaic design. As described above, use of thequarter parabola trough configuration of FIG. 1F permits the use of theclosed shaped truss under the reflector structure 107 and under thereflector panels 106. Furthermore, the quarter parabola troughconfiguration allows for the solar receivers 104 to be located at theedges of the reflector structure 107, as further described below withreference to FIG. 2A. The solar receivers 104 and all structuralelements such as the stand, support structure and frame thus do not casta shadow over the reflector panels 106, which results in a moreefficient solar energy collector 100.

Referring back to FIGS. 1B-1D, the dimensions of the collector units 100may be widely varied to meet the needs of particular applications. Byway of example, collector lengths L_(collector) on the order of betweenabout 5-6 meters (m) having at least three solar receivers 104 mountednear each top edge of the support structures 102 a, 102 b work well formany applications. In such systems optical aperture widths (W1) in therange of about 800-1200 millimeters (mm) with an optical aperture 101 a,101 b separation (W2) of between about 15-250 mm work well. Thus, thetotal width of the collector may be between 2-3 m. The height (H1) ofeach trough from bottom 124 to top edges 103 of the support structure102 may be between about 300-400 mm. The top edges 103 may also lie in alongitudinal plane 140 of the collector. In one specific example,L_(collector) may be 5.7 m, W1 may be 1010 mm, W2 may be 200 mm, thetotal width of the reflector structure 107 may be 2.25 m, H1 may be 360mm, and the outer receiver support rails 204 (FIG. 2A) may have a widthof 15 mm. To achieve the approximate quarter parabola curvature agenerally planar panel may be elastically deformed to deviate fromplanarity from between about 10 to 40 mm. Although some specificdimensions are mentioned herein, it should be appreciated that thedimension of the collectors are in no way limited to these ranges.Rather, they can be widely varied to meet the needs of a particularapplication.

As illustrated in FIG. 1D, a plurality of braces 142 may be used toattach the shaping ribs 216 to the receiver support rails 202 on thesupport structure 102. The braces 142 may provide for additional supportand strength to the collector 100 as further discussed below.

FIGS. 2A and 2B illustrate an expanded perspective view of the exemplarysolar energy collector. As seen therein, the reflector structure 107 hasa plurality of shaping ribs 216. The shaping ribs 216 may provide boththe correct optical shape and the structural stiffness for the reflectorpanels 106. The surface of the shaping ribs 216 adjacent to reflectorpanels 106 is formed to resemble the quarter parabolic configuration orshape. The shaping ribs 216 may approximately resemble a quarterparabolic shape to achieve an adequate focus of sunlight on solarreceivers 104. For example, in one embodiment the surface of the shapingribs 216 adjacent to reflector panels 106 may be formed to approximatean arc of a circle or other shape that provides suitable concentrationat the receiver. Although the shaping ribs 216 are illustrated below theedge of the reflector panels 106, the location or positioning of theshaping ribs 216 is not meant to be limiting as the shaping ribs 216 maybe located at any longitudinal position to support the reflector panels106.

The shaping ribs 216 may be formed as a single dual trough structurefrom a sheet stock by water jet cutting, laser cutting, stamping, or anyother suitable means. The sheet stock may be of any form. For example,the sheet stock may be a planar, rectangular sheet stock. In anotherexample, the sheet stock may be formed into a “T” shape, “D” shape, “L”shape, “C” shape, or any other similar shape that provides for a higherstiffness and stronger shaping rib. In another embodiment, shaping ribs216 may be assembled from multiple pieces and coupled together via anymeans such as the use of structural adhesives, welding, bolts, and thelike. Furthermore, the shape of the shaping ribs 216 may minimize scrapduring production as most of the material in a rectangular piece ofsheet stock is used to form the shaping ribs 216.

The actual geometry of the shaping ribs may be widely varied. In someparticular embodiments suitable for use with collectors sized asdescribed above, each shaping rib 216 may have a height (H2) of betweenabout 20-120 mm and a thickness of 1 to 4 mm. In one example, theshaping rib 216 may be 40 mm in height, H2, and have a thickness of 1.5mm. In some embodiments, the shaping rib 216 may be thicker at thebottoms 124 and thinner near the top edges 103. Alternatively, shapingrib 216 may be a composite structure formed from multiple pieces ofsheet metal stock bonded together with any known means such as the useof structural adhesives, structural tape, welding, bolts, and the like.This may minimize weight and maximize strength of each rib 216 and thecollector 100.

The quarter parabolic configuration of the shaping ribs 216 allows forthe shaping ribs 216 to be made from lighter, lower-cost structuralmaterial. Additionally, in one assembly procedure, flat reflector sheetsare bent to conform to the quarter parabolic configuration of theshaping ribs 216. As described above, one advantage of the quarterparabolic configuration is that it does not generate large stresseswithin the reflector when the reflector sheets are bent during assemblyto form the reflector panels 106. Furthermore, the support structure 102allows a single reflector panel 106 to be fabricated from a single,continuous reflector sheet for each half trough that extends along theentire length L_(collector) of the collector 100. Of course it should beappreciated that in alternative embodiments, each half trough can beformed from multiple reflector panels arranged side-to-side, end-to-endor in any configuration that completely covers the half trough.

In one embodiment, each reflector panel 106 may be made of Miro-Sun®KKSP, made by Alanod of Ennepatal, Germany. The Miro-Sun® KKSP is a 0.5mm thick aluminum strip that may have a specialty surface providing over90% specular reflection over the band in which silicon photovoltaiccells operate. A protective lacquer coating may be applied to the top ofthe reflector panels 106 to increase abrasion and weather resistance. Inanother embodiment, the reflector panels 106 may be made of any highreflection material, produced by Alanod or a plurality of other vendors.In still another embodiment, the reflector panel 106 may have a silvercoated polymer-based laminate over the aluminum strip. Once thereflective properties of the silver coated laminate are degraded fromweather and/or the sunlight, the silver coated laminate may be removedto thereby expose a new reflective layer. This allows the collector 100to be used for longer periods of time without having to be replaced,easily maintained, and less costly. A reflector panel may have betweenabout 1-5 layers of silver coated laminate.

The reflector panels 106 may be made in a continuous roll-to-rollprocess having a width of 1250 mm. Each reflector panel 106 may beformed by using an entire roll width, or one-half or one-third of thewidth of the roll thereby reducing any waste as the entire roll may beused to form the reflector panels. In one example, the reflector panels106 may be a half-width slit roll having a width of 625 mm, which formsa reflector panel having a length substantially equal to L_(collector)and a height substantially equal to H1. In another example, the lengthmay be 5.7 m and the height may be 360 mm. In one embodiment, eachreflector panel may be formed from a plurality of reflector sheets, eachsheet being fabricated from a roll of reflector material in such a wayto substantially utilize all the reflector material on the roll withminimal waste.

In another embodiment, the reflector panels 106 may be made of atempered thin glass mirror bonded to a suitable backing. The mirror mayhave a thickness of between about 0.10 mm to 1 mm. The quarter parabolicconfiguration curvature of the reflector panels 106, when elasticallydeformed to conform on the support structure 102, is less than thecurvature of a traditional full parabola configuration allowing use ofthe tempered thin glass mirror. In one embodiment, the reflector panels106 may have a silver coated laminate over the mirror as discussedabove.

In yet another embodiment, the reflector panel 106 may have a backingpanel attached to the reflective surface (not shown) to stiffen thepanel assembly. In one example, the backing panel may be a sheet ofaluminum or similar material. In another example, the backing panel mayhave a complex structure, such as a honeycomb, X-shape, V-shape, or thelike. The backing panel may have a thickness of between about 0.5 mm to5 mm.

In yet still another embodiment, the reflector panels 106, supportstructure 102, and frame 108 may all be made of the same material, suchas aluminum. Use of the same material may ensure a similar coefficientof thermal expansion (CTE) that allows for the use of large areareflector panels without deleterious mechanical deformation. Asillustrated and described above with reference to FIG. 1B, eachcollector 100 may have four reflector panels 106 that each run the fulllength L_(collector) of the collector 100. This provides for easierassembly of the collector 100 and for a stiffer overall structurecompared to current solar energy collectors. Current collectors mustinstall shorter reflector panels or strips to accommodate for the CTEmismatch between the frame and the reflector because the CTE mismatchmay cause deformation and potential permanent mechanical damage asdiscussed above.

As described above and below in detail, in some existing designs, stripsof the reflector panels may cast a shadow on the solar cells. Any shadowon the solar cell may reduce the overall concentrator efficiencydisproportionately due to the nature of the electrical connection amongthe solar cells as the solar cells may be connected electrically inseries. The efficiency may decrease by the ratio of shadow width to cellwidth and not by the ratio of shadow width to aperture length. Forexample, a 5 mm wide gap or non-reflective section between the strips ofreflectors may cast a shadow at least 5 mm wide on a cell 78 mm wide,leading to an overall efficiency decrease of 5/78 or 6.4%.

In the illustrated embodiment, the frame 108 has a plurality of crossbeams 212 and at least a pair of parallel support bars 214. The parallelsupport bars 214 may be elongated, longitudinal structures formed froman extrusion. In another embodiment, the parallel support bars 214 mayhave a plurality of elements, such as additional parallel support bars,coupled together such as with the use of structural adhesives, welding,soldering, brazing, and the like to form the single parallel support barfor the frame 108. Alternatively, the parallel support bars 214 may bemade stronger with other structural devices such as angled brackets,elongated rods positioned within the center of the parallel support bars214, and the like. The cross beams 212 may be any member joining thesupport bars 214 to provide structural support and bracing between thesupport bars 214. The frame 108 may be coupled to the bottoms 124 a and124 b of the support structure 102 and shaping ribs 216 to providestructural support for the collector 100. In one embodiment, the crossbeams 212 are T-sections as illustrated in FIGS. 2A and 2B and may besubstantially equal to the number of shaping ribs 216. The cross beams212 may be formed from an extrusion. In another embodiment, the crossbeams 212 may be positioned to form various geometric shapes, such asjoining the support bars 214 at an angle thereby forming a triangle asillustrated in FIGS. 1A and 1B. Thus, the placement of the cross beams212 is not meant to be limiting as the cross beams 212 may be placed inany position along the support bars 214 such as an X-shape, and thelike.

The frame 108 may connect to the reflector structure 107 via the bottoms124 a, 124 b to form the closed trapezoidal torque tube structure 136 asdescribed above. In one embodiment, frame 108 may be coupled to thesupport structure 102 via opening 306 (FIG. 3C) with a bolt, screw,mating tabs and slots, or any other similar known means. Additionalhardware, such as lugs, may be used to couple the frame 108 to thereflector structure 107 as further discussed below. In anotherembodiment, frame 108 may be coupled to the reflector structure 107 bybeing welded together, or by any other means. The frame 108 may have alength substantially equal to or slightly less than L_(collector) and awidth (W4) of between about 800-1400 mm. In one embodiment, W4 may be1300 mm.

While the frame 108 shown in FIG. 2B is planar, this is not intended tobe limiting as the frame may have a non-planar configuration. Forexample, the frame 108 may have a V-shape, which increases the effectivediameter of the torque tube created when frame 108 is coupled toreflector structure 107. This increases the torsional stiffness of thecollector 100.

As illustrated in FIG. 2A, the support structure 102 may have innerreceiver support rails 202 a, 202 b and outer receiver support rails 204a, 204 b. The inner receiver support rails 202 a, 202 b and outerreceiver support rails 204 a, 204 b may be oriented perpendicular to theshaping ribs 216 and attached to the top ends of each support rib 216.Each receiver support rail 202, 204 may be configured to receive solarreflectors 104 as described in detail with reference to FIGS. 3A and 3B.In one example, each top rail 202, 204 may be configured to slideablyreceive a solar receiver 104 in a longitudinal direction as illustratedby arrow A. In another example, solar receivers 104 may be coupled toeach top rail 202, 204 by any means that allows for differential thermalexpansion between the solar receivers 104 and each top rail 202, 204.Solar receivers 102 may be coupled to reflector structure 107 in such amanner to allow removal or installation of a middle receiver withoutremoval of adjacent receivers.

FIGS. 3A-3D illustrate detailed sections of the collector illustrated inFIG. 2B. FIGS. 3A and 3B illustrate a detailed view of section 220 ofFIG. 2B. FIG. 3A illustrates a detailed view of 220 of FIG. 2B withexemplary solar receiver 312 a, 312 b as described with reference toFIG. 4D. FIG. 3B illustrates a detailed view of 220 of FIG. 2B with anexemplary dual sided receiver 300 as described with reference to FIGS.4D. Dual sided receiver 300 may have a plurality of solar cells 316 ontwo opposing sides and a heat sink 318 located between the solar cells316. FIGS. 3A and 3B illustrate the inner receiver support rails 202 a,202 b of support structure 102. The upper edges of each reflector panel106 may be received by an attachment member 302. The attachment member302 may be formed in the top rail 202, 204 as part of support structure102. The attachment member 302 may have a slit, groove, or any othertype of receiver to receive and support the upper edge of the reflectorpanel 106.

The receiver support rails 202 may be coupled to the shaping ribs 216and support structure 102 at a notch 314 formed between the troughs 120a, 120 b. The receiver support rails 202 may be coupled to the shapingribs 216 by any known means such as with the use of structuraladhesives, welding, soldering, brazing, and the like. Additionalhardware, such as lugs, brackets, braces (142 illustrated in FIG. 1D)and the like may be used to attach the shaping ribs 216 to the receiversupport rails 202. Brace 142 may be used to provide addition stiffnessfor the connection between the shaping ribs 216 and the inner receiversupport rails 202. Shaping ribs 216 are positioned along the length ofcollector 100 at regular intervals to provide mechanical support anddefine the optical shape of reflection panels 106. Typical rib-to-ribspacing may be between about 200 mm to 800 mm. In one embodiment, therib-to-rib spacing is about 550 mm. The shaping ribs at the ends of thecollector 100 may also be set back from the reflector panel 106 sideedges to provide space for coupling structures and mounting posts, asdefined in more detail below. The attachment member 302 may serve as astructural element, provide shape for the reflector panels 106 byconstraining the upper edge of the reflector panels 106. The receiversupport rails 202, 204 may serve to aid in the installation of thereflector panels 106, and provide a stress-free sliding interface forthe solar receivers 300, 312 by allowing the solar receivers 300, 312 tobe easily slideably received by the receiver support rails 202, 204.

FIG. 3C illustrates a detailed view of section 222 of FIG. 2B. In theillustrated embodiment, each shaping rib 216 has a groove 304 to receivea bottom edge protector 308. The bottom edge protector 308 extendslongitudinally substantially near the bottom 124 of the entire length ofsupport structure 102. The bottom edge protector 308 may have a slit,grove, notch, or any other type of receiver to receive and support thebottom edge of the reflector panel 106. Reflector panel 106 may be pressfit into the edge protector 308 or be attached to the edge protector 308by any suitable means including use of structural adhesives, welding, orbrazing, or similar means. As further illustrated in FIG. 3C, a drainagegap 110 may be formed between the lower edges of each reflection panelto allow any moisture or water to drain through the collector 100. Thewidth (W5) of the drainage gap 110 may be between about 5-20 mm. In oneembodiment, W5 may be about 10 mm.

In one embodiment, the reflector panels 106 may be affixed to thesupport structure 102 by any known means such as the use of structuraladhesives, welding, soldering, brazing, bolts, screws, or the like. Thisallows for the reflector panels 106 to resist shear and the stiffness ofthe collector 100 increases. Unlike traditional full parabolacollectors, the quarter parabolic configuration may be able to withstandhigher shear loads before buckling due to its lower curvature.Additionally, for the same system design load, a wider spacing betweeneach shaping rib 216 may be possible.

When reflector panels 106 are held and supported by support structure102 between attachment member 302, bottom edge protector 308, andagainst shaping ribs 216, the reflector panels 106 are bent with acurvature having a substantially quarter parabolic configuration. Thisquarter parabolic configuration enables sunlight 135 to be directedtowards the solar receiver 104 using a single reflection as illustratedin FIG. 1F. Use of only a single reflection improves the collectoroptical efficiency compared to multi-reflection systems. Current dualtrough solar collectors typically require more than one reflection bythe sunlight before being received by a solar receiver.

FIG. 3D illustrates an exemplary lug 310 that may be used to attach theshaping ribs 216 to the frame 108. Although illustrated attaching theshaping ribs 216 to the frame 108, the lug 310 may also be used toattach the shaping ribs 216 to the undersides of the receiver supportrails 204 of the structural support 102. The lug 310 may be “T” shapedsuch that the lug 310 may be slideably received by the frame 108 asillustrated. Since the lug 310 may easily slide into the frame 108and/or undersides of the receiver support rails 204, the use of the lugs310 provides for easy assembly. The lug 310 may have a slit 312 toreceive a shaping rib 216. In use, the lug 310 may have a plurality ofopenings 306 to match the openings (not shown) in the shaping rib 216such that an attachment member, such as a screw, bolt, rod, or the likemay be received by the openings 306 to secure the shaping rib 216 to theframe 108.

In one embodiment, the lug 310 is coupled to the frame 108 and/orundersides of the receiver support rails 204 via a structural adhesive.The structural adhesive may be injected into the joint through theopenings 306 and may flow across the joint covering all mating surfaces.No trapped air spaces are present using this technique providing uniformcoverage of the adhesive and a consistent repeatable adhesive bondthickness between the frame 108 and the underside of the lug 310. Thisprovides for a strong bond attachment of the lug 310 to the frame 108.

FIGS. 4A-4E illustrate exemplary embodiments of a solar receiver. Eachcollector 100, as illustrated in FIG. 1A and 2A, may have outer solarreceivers 104 a positioned on the outer receiver support rails 204 ofthe collector 100 and inner solar receivers 104 b positioned on theinner receiver support rails 202 of the collector 100. Each solarreceiver 104 may have a length less than the length L_(collector) of thecollector 100. The solar receiver length is chosen so that an integralnumber of receivers, positioned longitudinally adjacent to each otherwith a minimal gap, have a length substantially equal to L_(collector).For exemplary purposes only and not intended to be limiting, ifL_(collector) is about 5.7 m, and three receivers are used, the lengthof the solar receiver 104 may be about 1.897 m. Additionally, each solarreceiver 104 may weigh between about 15-45 pounds (lbs) to allow forease of assembly, maintenance, and removal. In one embodiment, theweight of each solar receiver may be about 30 lbs.

Referring to FIGS. 4A and 4B, an exploded view of the solar receiver,each solar receiver 104 may have a base plate 408, a first encapsulantlayer 404 a above the base plate, a plurality of PV or solar cells 406above the first encapsulant layer 404 a, a second encapsulant layer 404b above the plurality of solar cells 406, and a top protective sheet 402above the second encapsulant layer 404 b. The solar receiver 400 may beformed by any known process, such as lamination, and the like.Lamination is a process that consists of heating the solar receiverstack and applying pressure to fuse all the components together to forma laminate receiver structure. The lamination process may also occur ina vacuum environment to reduce air bubbles.

The base plate 408 may provide a backing for the plurality of solarcells 406 during lamination. The base plate 408 may be formed of anextruded metal, for example, aluminum, an extruded metal filled polymer,or any similar material. In one embodiment, the base plate 408 may beformed with mechanical features 420 extending outwardly from the baseplate 408 to mechanically capture and position each of the solar cells406. The base plate 408 may be wide enough to receive each of theplurality of solar cells 406. In one embodiment, the width of the baseplate (W6) may be between about 80-85 mm. The base plate 408 may have amating feature 412 to engage the rails 202, 204 as discussed in detailedbelow with reference to FIG. 8. The mating feature 412 may have a width(W7) of between about 15-50 mm. Alternatively, as shown in FIG. 4E, baseplate 408 may have a plurality of clips 508 (FIG. 5) or other mechanicaldevices positioned below solar cells 406 to facilitate attachment ofbase plate 408 to rails 202 and 204. The length of the base plate 408,L_(baseplate), may define the length of the solar receiver 400 and maybe between about 1.0-6.0 m. In one embodiment, L_(baseplate) may beabout 1.897 m.

The base plate 408 may have a low mass such that it allows for a reducedlamination cycle time as compared to traditional solar receiverlamination processes. In some embodiments, the base plate 408 has alayer of a thin conformable dielectric coating applied to provideredundant electrical insulation. The dielectric coating may be any knownpolymer and may be applied as a liquid or powder. The dielectric coatingmay be applied to the base plate 408 by any known means such as baking,painting, and the like. The dielectric coating may be thin to maintain ahigh thermal conductivity and may be between about 20-100 microns.

The first and second encapsulant layers 404 a, 404 b provide electricalisolation between the plurality of solar cells 406 and the base plate408 to prevent conduction from the base plate 408 and electricalshorting of the plurality of solar cells 406. The encapsulant layers 404may also protect the plurality of solar cells 406 from weather andmoisture. Additionally, the encapsulant layers 404 may compensate forany differential thermal expansion between the plurality of solar cells406 and the base plate 408.

The encapsulant layers 404 may be made of thermo-polymer urethane (TPU),ethylene vinyl-polymer acetate (EVA), or any other similar materials.TPU is particularly well suited for use in solar applications because itis more resistant to ultra violet (UV) radiation than traditional EVAmaterials, which is particularly important in receivers utilized inconjunction with solar concentrators because the ultra violet radiationis concentrated as well. The encapsulant may be a poured orthermoplastic silicone that has a high light transmissibility andstability under more intense UV light.

The top protective sheet 402, although optional, may protect theplurality of solar cells 406 from moisture, air, contaminates, and thelike. The top protective sheet 402 may be formed of any protectivematerial such as glass, Teflon® (such as DuPont Teflon Tefzel®, amodified ethylene-tetrafluoroethylene fluoropolymer (ETFE)), or anyother similar materials. An optional anti-reflection or spectrallyselective coating can be applied to the outer and/or inner surface oftop protective sheet 402 to improve collector efficiency. In oneembodiment the, the top protective sheet 402 may be a thin,chemically-tempered glass having a thickness of between about 0.1 mm to1 mm. In another embodiment, the glass may be a thick,thermally-tempered glass having a thickness of about 1 mm to 3 mm.

The top protective sheet 402 may be fabricated from a number of panes toreduce stress induced by differential thermal expansion between the topprotective sheet 402 and the base plate 408. The individual panes in thetop protective sheet 402 may have a small gap or expansion joint betweenthem to allow for the differential thermal expansion. This gap may bebetween about 0.2 to 2.0 mm. In one embodiment, the gap may be about 1.0mm.

In another embodiment, the gap between the panes may be sealed with abarrier material such as silicon, epoxy, butyl, or any other similarmaterial that is compliant, optically transmissive, and seals outmoisture and water.

Base plate 408, encapsulant layers 404, solar cells 406, and topprotective sheet 402 may each have a thickness of between about 0.01-3.0mm to provide for a low cost and light weight solar receiver 400. Forexample, the top protective sheet 402 may weigh less and be thinner thantraditional 4 mm thick glass top protective sheets used in one suncollectors.

Each of the plurality of PV or solar cells 406 may be connectedelectrically in series to form a solar cell string 410 having a cellstring axis 436. The solar cell string 410 may be formed by any knownmeans such as soldering each solar cell together via interconnect wires414. Each solar cell 406 may have a cell size of about 78×78 mm and maybe a square wafer manufactured from a monocrystalline silicon boule.Alternatively, the solar cell may be any type of known solar cell suchas multi-crystalline, single-crystalline, rear contact, emitterwrap-through, LGBC (laser grooved buried contact), PERL (passivatedemitter with rear laterally diffused cell), multi-junction, siliconribbon, thin film PV cells, and the like. Although each solar cell 406is illustrated as a square, the shape of the solar cell 406 is notintended to be limiting as any shape may be used such as a rectangle,square with one or more rounded or truncated corners, hexagon, and thelike.

The plurality of solar cells may be modified such that they have a lowerseries resistance when electrically connected. In one embodiment, theback surface field strength of the solar cell may be increased and thetop-surface conductive grid may be thickened or increased in number toreduce the series resistance in traditional non rear-contact solarcells. In another embodiment, for rear contact PV cells, the backmetallization of the solar cells may be thickened.

Each solar cell 406 may be positioned with a small gap between eachother to allow room for electrical connections, differential thermalexpansion, and mechanical tolerances. A single solar receiver 400 mayhave any number of solar cells 406 to form a cell string. In oneembodiment, one solar receiver 400 may have about twenty four solarcells 406 and may be electrically connected in series, parallel, or anycombination. Each solar cell 406 when illuminated may generateapproximately ½ volt. Thus, if all cells are connected in series thesingle solar receiver 400 may generate a total of 12 volts.

A junction box 428 may be coupled to the solar cell string 410 viainterconnect wires 414. The junction box 428 may be positioned on thefront surface, adjacent to solar cell string 410, at each end of thesolar receiver 400. Placing the junction box 428 on the same side of thebase plate 408 as the solar cells string 410 facilitates electricalconnections between these elements and improves the manufacturability ofreceiver 400

FIG. 4B shows an exemplary electrical schematic of a section of thereceiver 400 wiring. In this example the individual solar cells areconnected electrically in series. The junction boxes are electricallyconnected at either end of the cell string. The junction box 428 may beelectrically connected to a junction box of an adjacent solar receiveron one side of the solar receiver 400 and may be electrically connectedto a second junction box located on the opposite end of the solarreceiver 400. In one embodiment, the junction box 428 may have a by-passdiode as further discussed in detail below. Some junction boxes mayfacilitate transfer of the power produced from each of the collectors100 to an electrical system, such as a power generation plant describedbelow, which may provide electrical energy for any end use. The junctionbox 428 thus facilitates an electrical connection between the receivers,provides strain relief for the cell string wiring, and allows for theaddition and use of other devices that may be necessary, such as abypass diode and the like.

FIG. 4C illustrates a back surface of the solar receiver 400. The solarreceiver 400 may have a grounding clamp 430 attached to the base plate408 or the mating feature 412 of the solar receiver 400 behind junctionbox 428. The grounding clamp 430 may provide an electrical path from thebase plate 408 to the structural support 102 via electrical wires 432.The wires may use 10 gauge copper wire. The structural support 102 mayin turn be connected to an earth ground, thereby grounding the receiver400 and protecting a user from any electrical short circuits that mayoccur. Although the grounding clamp 430 is illustrated behind junctionbox 428, the location is not intended to be limiting as the groundingclamp 430 may be positioned at any location on the base plate 408, suchas any other location on the back surface, the front surface, top, orbottom of the base plate.

FIG. 4D illustrates an exemplary solar receiver having a heat sink 416extending outwardly and coupled to the base plate 408 of the solarreceiver 400. The heat sink 416 may have a plurality of fins 418positioned vertically and perpendicular to the base plate 408. When thesolar receiver 400 is coupled to the receiver structure 107, theplurality of fins 418 may be substantially perpendicular to the frame108, longitudinal plane 140, trough or optical apertures 101, thelongitudinal axis 162, and the bisecting plane 105. The heat sink 416allows heat generated in the solar cells 406 to dissipate upwardly bynatural free convection through the plurality of fins 418 withoutobstruction or interference from the solar cell string 410. Thisminimizes the temperature rise experienced by solar cells 406 improvingefficiency and prevent warping, electrical shorts, or any othermalfunction due to high temperatures. This embodiment may be used inboth the outer solar receivers 104 a and inner solar receivers 104 b asillustrated in FIGS. 1A and 1B. Use of this embodiment as an inner solarreceiver 312 a, 312 b is also illustrated in detail in FIG. 3A. Thisallows for easier manufacturing as only one solar receiver configurationneeds to be manufactured for the collector 100.

FIG. 4E illustrates another exemplary solar receiver having a commonheat sink 416 coupled between two solar cell strings 400 a, 400 b. Thisembodiment may be used as the inner solar receiver 300 as illustrated indetail in FIG. 3B. The heat sink 416 may be used to allow heat generatedfrom the solar cell strings 400 a, 400 b to dissipate upwardly bynatural free convection through the plurality of fins 418 to maximizeoperating efficiency and prevent warping, electrical shorts, or anyother malfunction due to high temperatures. Furthermore, the heat maydissipate upwardly without any obstruction or interference from thesolar cell strings 400. This embodiment allows for easier assembly as auser will only need to attach a single inner solar receiver 300 onto thereflector structure 107.

Although the illustrated solar cells are positioned on the base plate asa single linear row of cells this is not intended to be limiting. Forexample, two rows of solar cells may be positioned one above the other.A two row receiver would allow a control system to track the powerproduced by each row to determine whether the collector is correctlyaligned. Should the same power be generated from each of the solar cellrows, the collector would be properly aligned. If the power generatedfrom each of the solar cell rows are different, the collector may berotated about the pivot axis, as further discussed below, to ensure itis properly aligned with the sun and used efficiently.

FIG. 5 illustrates an exemplary heat sink. The heat sink 500 ispositioned on the back of the base plate 408 opposite from the cellstring. The heat sink 500 has a plurality of interconnected fins 502 toform the heat sink 500. Each plurality of fins 502 may have a width (W8)that is substantially equal to the width of base plate 408 (W6+W7) ormay be between about 25-150 mm. The height (H_(fin)) may be betweenabout 25-150 mm.

The heat sink 500 may have a plurality of interconnected fins 502created by forming a continuous roll of material to form a serpentineconfiguration. This eliminates the need to assemble a heat sink usingindividual fins and is low cost and easy to manufacture. Furthermore,heat sink 500 may be coupled to the base plate 408 after the solar cells406 have been installed on the base plate 408 and the base plate/solarcell assembly laminated together as a single unit. This may obviate theneed for the lamination process to accommodate the heat sink, therebyallowing use of standard lamination equipment. The heat sink 500 may becoupled to the back of the base plate 408 by any known means such aswith the use of structural thermal adhesives, bolts, screws, swaging,staking, welding, soldering, brazing, and the like.

As illustrated in FIG. 5, in one embodiment, the solar receiver 512 mayhave clips 508 to facilitate attachment to the reflector structure 107.The clips 508 may allow the solar receiver 512 to be slid along the toprails 202, 204 or removably attached to the top rails 202, 204 by snapfit, pressure fit, or any other means. This allows a user to easily,efficiently, and quickly remove a solar receiver 512 without having toslideably remove any adjacent receivers. Additionally, use of the clips508 may provide for good thermal insulation between the solar receiver512 and the reflector structure 107 as there is only a small contactarea between the solar receiver 512 and reflector structure 107.

FIGS. 6A and 6B illustrate another exemplary heat sink. The heat sink600 has a plurality of non-interconnecting, individual fins 602. Theback of the base plate 408 may have a plurality of tapered grooves 604cut into it to receive each of the plurality of individual fins 602. Toassemble, in one embodiment, the heat sink 600 and the base plate 408are press-fit together. A fin plate 608 may be used to engage the fins602 to prevent buckling during the press-fit process. The plurality ofsolar cells may thus be subjected to the full pressure required for apress fit, whereby the base plate 408 provides the support necessary tosupport each solar cell evenly to prevent cracking of the solar cells.In another embodiment, the heat sink 600 and the base plate 408 may becoupled together by the use of structural adhesives, bolts, screws,welding, soldering, brazing, and the like.

As stated above, fin plate 608 may prevent warping of the base plate408. During the press fit, the back surface of the base plate 408 may beput into compression from the plurality of fins 602, which may cause thebase plate 408 to bow and become concave on the solar cell side. Thus,the fin plate 608 may constrain the far ends of the plurality of fins602 and each plurality of fins 602 applies a small reaction moment alongthe far edge of each fin 602 which may prevent such bowing. This heatsink 600 design or configuration places the base of the fins 602 closeto the solar cells to minimize the heat flow resistance between thesolar cell and fins. In one embodiment, the heat sink fins 602 may bebetween about 1-15 mm away from the cell string.

FIGS. 7A-7C illustrate yet another exemplary heat sink. FIG. 7Aillustrates a perspective view of a fin 702 of the exemplary heat sink700. The heat sink 700 may have a base 704 having step-shaped edges 706extended outwardly from the sides 708 of the fin 702. FIG. 7Billustrates a plurality of fins 702 coupled together. The step-shapededges 706 are configured to stack against the step-shaped edges 706 ofother fins 702, yet keeping a space between them to form the heat sink700. The fins 706 may be coupled together by any known means such aswith the use of structural adhesives, bolts, screws, welded together, orthe like. FIG. 7C illustrates the heat sink 700 coupled to a base plate408. This embodiment may allow for the use of a base plate 408 that ismade of a flexible foil that may be an intermediary between the cellstring and the plurality of fins 706. This may reduce cost and weight ofthe solar receiver 710. Furthermore, the solar receiver 710 may have alower thermal resistance since the thickness of the base plate has beendecreased.

In one embodiment, the fins 602, 502 may have slits, grooves, cuts,openings, or the like (not shown) to provide an increase in heattransfer from the fins to the air as well as provide for a lighter solarreceiver.

FIG. 8 illustrates an exemplary attachment of a solar receiver 800 to atop rail 202 of the reflector structure 107. The solar receiver 800 isillustrated using the heat sink of FIG. 5A. The solar receiver 800 maybe slideably coupled to the support structure 102. The mating feature412 of the solar receiver 800 may be slid along top rail 202.Alternatively, solar receiver 800 may be coupled to top rail 202 usingclips 508, screws, split-clamps, sliding detents, mechanical interfacesor some combination of these items to allow installation and removal ofreceiver 800 without removal of adjacent receivers. The design ofreceiver shown in FIG. 4E may facilitate this type of coupling. When thesolar receiver 800 is aligned to the sun to begin operation, the solarreceivers 400 may heat up to between 10° to 30° C. above the ambienttemperature, the exact temperature rise depending on the wind and solarinsolation. This temperature rise may cause the length of the solarreceivers 400 to increase from thermal expansion. However, thetemperature rise of the mating feature 412 and top rail 202 will beless, since they are not directly exposed to concentrated sunlight andthey are in poor thermal contact with the receiver. In one embodiment,the solar receivers may be positioned next to each other with a nominalgap of between about 0.01 to 10 mm to accommodate for thermal expansion,electrical interconnections, and mechanical tolerances without anystress to each solar receivers 800.

The solar receivers 800 may be positioned such that the cell string issituated in front of the optical focus of the reflector panels 106 (FIG.1F). This avoids extreme concentration areas of sunlight on cells thatcould damage the cell and deleteriously affect its performance. This mayalso avoid bringing the sunlight to a focus in front on the solarreceiver, which may pose a safety hazard. The face of each solar cell isalso perpendicular to the trough aperture and parallel to thelongitudinal axis.

As discussed above, the dual trough configuration used in this inventionallows for less shadow over the collector as the solar receivers may bepositioned on the top sides or edges of the collector. Moreover, havingthe closed truss below the reflector panels eliminates shadow formationon the reflector panels. However, should there be a shadow over one ormore of the solar cells or if one of the solar cell malfunction, thecells in the string become mismatched and the output of the cell stringdrops precipitously. If the solar cells 406 are connected in series,current through all the solar cells in a string must be the same,implying that the current from the cell string is equal to the lowestcell current.

To account for a possible cell mismatch, a bypass diode may be used. Anyknown bypass diode may be used to protect the solar cells from thermaldestruction and maintain useful power output in case of total or partialshading, broken solar cells, or cell string failures. In one embodiment,a single bypass diode may be coupled to each individual solar receiver104. In another embodiment, a bypass diode may be coupled to each solarcell 406 or a group of solar cells in each solar receiver 104. In yetanother embodiment, a bypass diode may be coupled to a series ofconnected solar receivers. In use, the bypass diode may determinewhether a solar cell or group of solar cells is limiting the output anddivert current around the limiting solar cell or cells. In one example,if the threshold current is not met due to shadows, solar cell failure,or any other reason, the bypass diode may allow the current to flowaround the cell string thereby preventing a loss of output power.

The economic viability of a solar photovoltaic system is dictated notonly by the collector design, but also by the costs associated inmanufacturing the various system components, with shipping the system tothe operating site, installing the system, and maintaining and operatingthe system once it is installed. FIGS. 9A-9C illustrate an exemplaryshipping container that contains a kit suitable for assembling a groupof the solar energy collectors. Several standard shipping containers,such as a twenty or forty foot container may also be used. As anexample, FIG. 9A illustrates a perspective view of one twenty footequivalent unit (TEU) container packed with twenty-five collectors.Internal dimensions of a TEU may be about 5.8×2.3×2.3 m with a volume ofabout 33 m³. The maximum payload may be about 21,710 kilograms (kg). Thesolar receivers 902, reflector structure 904, and frames 906 arepackaged and shipped separately in the TEU container and assembled onsite. Site attachment of these components allows efficient shipment tothe installation site, since the components can be nested togetherwithin a standard shipping container. FIG. 9B illustrates a detailedview of 908 of FIG. 9A. FIG. 9B illustrates that when the reflectorstructures 904 are stacked together, the rails 912 bear the weight ofthe stack during shipment and helps prevent scratches on the reflectors914. FIG. 9C illustrates a detailed view of 910 of FIG. 9A. FIG. 9Cillustrates an exemplary configuration to stack the frames 906. Thecross sections or T-sections 916 of the frames 906 enables the frames906 to be nested during shipping by flipping and staggering every otherframe 906.

An alternative to shipping the various collector parts within a singlecontainer is to ship different collector parts in different containers.As in the previous example, standard shipping containers, such as TEUcontainers, may be used. This shipping method facilitates amanufacturing production system where different collector components canbe manufactured at different locations then shipped to the installationsite. For example, the receivers 902 require a relatively sophisticatedmanufacturing process and their production could be located in an areawith a skilled workforce. The reflector structure 904 and frames 906require less sophisticated manufacturing techniques and their productionmay advantageously be located in an area with lower labor costs, closeto the panel manufacturing location, and/or close to the installationsites. Using this alternative manufacturing and shipping system mayallow minimization of the entire solar photovoltaic system cost.

FIGS. 10A-10D illustrate an exemplary power generation plant inaccordance with an embodiment of the invention that utilizes an array ofsolar energy collectors. The dual-trough design allows the structure ofthe collectors to be supported at a pivotal axis 1002 located in betweenthe two troughs 1014 a, 1014 b. The pivotal axis 1002 may be located inthe bisecting plane 105 (FIG. 1C) at or near the collector 100 center ofgravity. The center of gravity may also be located in the bisectingplane 105 slightly below the longitudinal plane 140 (FIG. 1C). The exactlocation of the center of gravity depends on the weights of thereceivers 902, reflector structure 904, and frame 906. This is differentfrom single-trough designs in which the pivot must be placed either infront of or behind the reflector. The single trough is eithercantilevered from a pivot behind the reflector, or supported with apivot at the center of gravity, which is located in front of thereflector. In cantilevered single-trough designs, either large torquesmust be transmitted from the tracking actuator along the structure ofthe trough or expensive and cumbersome counterweights must be used. Whensupported with a pivot at the center of gravity, the posts must extendabove the reflector requiring regular gaps in the reflector toaccommodate the posts. Both the post section protruding beyond thereflector plane and the gaps in the reflector itself will cast shadowson the cells. The dual trough configuration eliminates this problem byplacing the pivot axis both behind the reflector and very near thecenter of gravity of the collector. Nominally, the collector 1000 mayrotate through 120 degrees with the pivot within 10 centimeters (cm) ofthe center of gravity. However, the collector 1000 may also rotatethrough larger angles with the pivot farther than 10 cm away from thecenter of gravity.

The designer of a particular dual-trough system may make a smalltrade-off between range of motion and torque. To increase the range ofrotation, the pivot may be moved back, away from the center of gravityand longitudinal plane 140, at the cost of increased holding torque.Conversely, by placing the pivot at the center of gravity, a design withzero holding torque and slightly decreased range of motion is possible.Moving the pivot permits optimization of the collector for theparticular installation. For example, in a ground installation whereland is cheap, the increased structure spacing and increased range ofmotion may permit operation for a longer fraction of the day at the costof a marginally stiffer structure and tracker. However, for a rooftopinstallation where rows might be spaced more tightly a balancedconfiguration may be used to minimize structure and tracking weight.

The dual trough configuration brings both the center of gravity and thepivot axis 1002 close to the apertures 101 of the solar receiver. Thecenter of gravity may pass through or be located near the pivot axis1002 and the bisecting plane 105 (FIG. 1C). When stowed in a low-dragconfiguration with the aperture horizontal, this allows the overallstructure to be lower than a traditional full parabolic trough of thesame aperture. The lower height may result in lower bending moments inthe collector support post 1018 from wind loads.

The collectors or modules 1000 may be installed in rows as long asallowable to minimize end losses. Furthermore, the solar receivers neednot be coupled to the entire length of the collector. For example, onthe side away from the incident sunlight, sunlight is reflected out ofthe end of the trough and not captured on a solar receiver. Likewise, onthe side facing the incident sunlight, some light which does not passthrough the aperture may be received by the receiver. On the side facingthe incident sunlight, the first receiver closest to the incidentsunlight may receive no or only partial sun. As such, the first receivermay be omitted in this collector.

Module rows may be spaced approximately 2.4 times the collector width toreduce shading from adjacent rows. FIG. 10A illustrates a perspectivetop view of an exemplary power generation plant 1001 that utilizes anarray of solar energy collectors placed in a plurality of rows. In thisexample, the collector field consists of 4 rows of collectors 1000 witheach row containing 6 collectors 1000. The rows are spaced apart toavoid shadowing of the adjacent collectors as the collectors tracks thesun throughout the day. A single tracker mechanism can drive eachcollector in a row and/or multiple rows. Within any row the collectorshave a minimal gap between, on the order of several mm or less,minimizing shadowing of the receivers. No mechanical features obstructsunlight to any collectors in the field. The energy collected from allthe collectors 1000 may be transmitted through the junction boxes 428(FIG. 4A) and transmitted to any known electrical system 1020 to provideelectrical energy for any end use.

FIGS. 10B through 10D illustrate two rows of modules rotating about thepivot 1002 to remain oriented to the sun during the day. A trackermechanism may have a fixed track 1006, sliding link or track 1008, and atransfer link 1010. The fixed track 1006 may be oriented perpendicularto the collector rows and located below the plane of the collector 1000at the extent of rotation of the collector 1000. The fixed track 1006may provide a guide for the sliding track 1008, which may be actuated atone end by an actuator 1012. The sliding track 1008 may be coupled toeach transfer link 1010 by a pivot at a first end 1014. The far orsecond end 1016 of each transfer link 1010 may connect to the module1000 near the valley or bottom 1016 of one trough 1000 as illustrated.This linkage arrangement allows a single actuator 1012 to controlmultiple rows of collectors and to achieve the desired range of motionthroughout the day without losing too much leverage. FIG. 10Cillustrates an exemplary configuration in which the tracker linkage 1010has the most leverage over the module 1000 while FIG. 10D illustrates anexemplary configuration in which the tracker linkage 1010 has the leastleverage. The difference in torque of the transfer link 1010 about thepivot axis 1002 between the positions illustrated in FIG. 10B and FIG.10C is less than a ratio of 2 to 1 for a 120° range of motion. In analternative embodiment, the tracker mechanism may allow a range ofmotion between 90° to 160°. In one embodiment the range of motion may be140°. Aside from tracking the sun during periods of clear weather, thetracker mechanism is also used to orient the collector horizontallyduring adverse weather, for example a rain storm with strong winds. Thisorientation allows easy draining of water through drainage gap 110 andminimizes the wind load on the collector 1000.

The collector design facilitates installation at various types ofinstallation sites. For example, a field of collectors could beinstalled on the ground. Alternatively, a field could be installed on aroof top, particularly on a flat roof of a commercial building.Installation begins with rows of posts 1018 that have been installed ata spacing approximately equal to the collector length. Posts are locatedat the junction between two collectors. Collectively the plurality ofposts form a stand, which supports the collectors and allows them to berotated about the pivot axis. The gap between longitudinally adjacentcollectors 1000 may be nominal, for example between 0.5 and 10 mm.Minimization of the gap between longitudinally adjacent collectors 1000ensures a minimal shadow on the receivers. Alternatively, the collectorreflector surfaces may slidingly overlap each other to eliminate anyshadow. Unlike current concentrating solar PV modules, collectors 1000have no mounting hardware or support structure extending above thereflector panels.

In one embodiment to assemble the solar energy collector system, thereflector structure 107 may weight less than 240 lbs. and may be boltedto the posts 1018 at the tracker pivot 1002. The frame is then attachedto the reflector structure. Alternatively, the frame may be attached tothe reflector structure prior to the mounting of the reflector structureto the posts. Next, the twelve solar receivers are slid into place alongeach of the receiver support rails—three solar receivers on each rail.The solar receivers are connected electrically in series by a singleplug that contains two terminals for the string circuit and one for thestructure ground. After a collector is populated with receivers, thenext adjacent collector is installed and coupled to other adjacentcollectors using any known coupling structures. The coupling structuremay use a flexure to accommodate the longitudinal motion due to thermalexpansion while preserving high stiffness in all other directions. Thiscoupling process of all the collectors is continued until the desirednumber of receivers has been assembled and the appropriate electricalconnections between collectors made. The row length is determined by themaximum allowable twist and will depend on site layout, maximum designwind speed, and the tracker actuator used.

Once installed, each row will rotate throughout the day to track thesun. Tracking will orient the face of each solar cell so its surfacenormal is nominally perpendicular to the incident light entering theaperture of the collector. In other words, the solar cells are orientedso that essentially no incident sunlight directly strikes the solarcells, but the solar cells receive sunlight reflected off the reflectorpanels 106. The collectors 1000 may be oriented in any directionalthough most sites may utilize a North-South orientation. If thelongitudinal axis is oriented North-South, then the troughs maypartially shade adjacent troughs during summer early morning and lateafternoon, effectively reducing the field size by one-half. During thesetimes, the bypass diodes on the shaded receivers will allow thosereceivers that are not shaded to continue to produce electricity. Theheat sink performance will change depending on the angle of rotation ofthe module. For example, near mid-day when the sun is brightest, theplurality of air channels formed by the fins will be oriented nearlyvertical and the heat sink will operate with minimal thermal resistance,since the natural convective air flow through the heat sink air channelsis not obstructed by any photovoltaic cells or any other devices,elements, or features of the collector. Although the performance variesthroughout the day, the cell temperature will remain relativelyconstant. This is in contrast to current solar PV collector systems inwhich the fins are oriented in the least efficient direction at mid-dayand the most efficient in the morning and afternoon.

The solar receivers may require servicing, repairs, or the user may wantto upgrade the solar receivers to receivers using higher efficiencysolar cells. The modular design of the solar receivers allows for theease of replacement, repair, maintenance, and servicing of the solarreceivers. After a cell string has been electrically disconnected, asingle receiver may be uncoupled from the adjacent receiver(s) and slidout. When a new receiver is installed, the solar receiver may easily bere-attached to the adjacent solar receivers. Thus, the modular design ofthe collector 1000 allows for a lower cost and ease of maintenance,repair, replacement, or servicing of the collector. Furthermore, theremay be less maintenance required over a longer period of time comparedto current solar collector systems.

Example

The following example is for exemplary purposes only and is not intendedto be limiting as any number of solar cells may be used, the length ofthe solar energy collector may vary, and other embodiments may bepossible.

Referring back to FIG. 1A, the solar collector may have a lengthL_(collector) of about 5.7 m to allow for at least three solar receivers104 to be positioned on the top sides 202, 204 (FIG. 2A) of the supportstructure 102. The solar receiver as discussed above with reference FIG.4D may be used, which would allow for a total of twelve solar receivers.Each solar receiver 104 may have about twenty four solar cellselectrically connected in series. Since each solar cell may generateabout ½ volt, each solar receiver 104 may generate about 12 volts. Eachreceiver contains twenty-four solar cells so the total number of cellsin the collector 100 is 288.

The total optical aperture of the collector is the width of each trough(W1) multiplied by the trough length yielding an area of approximately11.4 m². Assuming a solar insolation of 1 kW/m² and a 17.5% collectorefficiency the collector will generate approximately 2 kW of electricalpower. To obtain this output power, standard silicon solar cellsproducing approximately ½ volt each will each generate slightly lessthan 14 amps of current.

In this design the optical concentration is a factor of approximately20:1, while the geometric concentration is a factor of approximately6.5:1. The approximately factor of three difference between the twovalues stems from increasing the solar cell size by approximately afactor of three to accommodate tracker misalignment and mechanicalerrors or deformation in the collector 100. This design requires only amodest tracking accuracy of +/−1.7° to achieve an optical efficiencywithin +/−10% of its maximum value. Such tracking accuracy is readilyachievable by standard methods.

While embodiments and applications of this invention have been shown anddescribed, it would be apparent to those skilled in the art having thebenefit of this disclosure that many more modifications than mentionedabove are possible without departing from the inventive concepts herein.For example, an actively cooled heat sink using flowing water, fluid, orair can be used in place of the passively cooled air heat sinkpreviously described. The energy contained in the flowing fluid may beused as a source of thermal energy. Alternatively, a heat pipe could beincorporated as part of the heat sink. While a dual trough collector hasbeen described many of the advantages of the edge collecting quarterparabolic reflector can be achieved with a single trough collector or amultiple trough collector, such as three, four, or even more troughs.Furthermore, although the receiver is described and illustrated with theuse of PV cells, other receivers are contemplated and may be used, suchas the use of fluids, hybrid PV and thermal systems, biocollection(algae slurry and the like) systems, other chemical and biologicalenergy systems, and the like.

1. A photovoltaic solar energy collector suitable for use in a solarenergy collection system that tracks movements of the sun along at leastone axis, the collector having an aperture and comprising: at least onereflector panel defining a reflector trough having a longitudinal axisand the aperture, there being a longitudinal plane that is substantiallycoplanar with the aperture; and at least one solar receiver, each solarreceiver including a plurality of photovoltaic cells having active cellfaces that are oriented substantially perpendicular to said longitudinalplane, wherein each solar receiver is positioned adjacent to a top edgeof the reflector trough.
 2. A photovoltaic solar energy collector asrecited in claim 1, wherein each reflector panel is arranged to directincident sunlight to the photovoltaic cells using a single reflection.3. A photovoltaic solar energy collector as recited in claim 1, furthercomprising a support structure that supports a plurality of thereflector panels, wherein the support structure supports the reflectorpanels in a manner that defines the reflector trough, the reflectortrough having the longitudinal axis, a trough base, a pair of reflectiveside walls and a trough aperture suitable for receiving incidentsunlight during operation of the solar energy collection system.
 4. Asolar energy collector as recited in claim 3, wherein the at least onesolar receiver is positioned outside the trough aperture such that theat least one solar receiver does not shade any of the reflective sidewalls during operation.
 5. A solar energy collector as recited in claim3, wherein the support structure supports a plurality of the reflectorpanels in a manner that defines a pair of adjacent reflector troughs. 6.A photovoltaic solar energy collector as recited in claim 3, whereineach solar receiver is positioned generally above an associatedreflective side wall and arranged to receive solar radiation reflectedfrom an opposing reflective side wall.
 7. A photovoltaic solar energycollector as recited in claim 3, wherein each reflector side wall has acurvature that resembles a segment of a parabola and is arranged todirect incident sunlight to a receiver positioned over an opposing sidewall using a single reflection.
 8. A photovoltaic solar energy collectoras recited in claim 1, wherein each solar receiver includes: a baseplate that carries at least one of the photovoltaic cells on a frontsurface of the base plate; and a plurality of spaced apart heat transferfins carried on a back surface of the base plate, wherein the finsextends outwardly from the base plate to define a plurality of air flowchannels that extend substantially perpendicular to the trough apertureand substantially perpendicular to the longitudinal axis.
 9. Aphotovoltaic solar energy collector as recited in claim 3, wherein: thetrough aperture has an aperture axis that is substantially perpendicularto the longitudinal axis; and the at least one solar receiver is aplurality of solar receivers, each solar receiver being positionedgenerally adjacent and above an associated side wall such that the solarreceivers do not shade the reflective side walls during operation in amode the tracks movement of the sun along one axis, each solar receiverincluding, a base plate, and at least one photovoltaic cell carried on afront surface of the base plate.
 10. A photovoltaic solar energycollector as recited in claim 9, wherein each of the plurality of solarreceivers further comprises a plurality of spaced apart fins extendingoutwardly from the base plate, and wherein the fins define a pluralityof air flow channels to receive an air flow, the plurality of air flowchannels extend substantially vertically when the trough aperture facesupward, and wherein the air flow is not obstructed by the plurality ofphotovoltaic cells.
 11. A photovoltaic solar energy collector as recitedin claim 10, wherein the fins have a serpentine configuration.
 12. Aphotovoltaic solar energy collector as recited in claim 11, wherein foreach receiver, a multiplicity of the receiver's fins are formed from acontinuous metal sheet.
 13. A photovoltaic solar energy collector asrecited in claim 9, wherein each receiver further includes an opticallytransparent encapsulant layer that covers the photovoltaic cellsassociated with the receiver and a transparent protective sheet thatcovers the encapsulant layer.
 14. A photovoltaic solar energy collectoras recited in claim 9, further comprising a plurality of receiversupport rails, each receiver support rail being coupled to the supportstructure and positioned generally adjacent an edge of an associatedtrough, wherein each receiver support rail slidably supports at leastone associated solar receiver.
 15. A photovoltaic solar energy collectoras recited in claim 14, wherein each receiver support rail slidablyreceives a plurality of solar receivers to support the receiver in amanner such that the receivers are thereby mechanically decoupled alongthe receiver support rails in a longitudinal direction.
 16. Aphotovoltaic solar energy collector as recited in claim 9, furthercomprising an insulating layer directly applied to the base plate andpositioned between the base plate and the photovoltaic cells.
 17. Aphotovoltaic solar energy collector as recited in claim 1, wherein theactive faces of the photovoltaic cells are oriented substantially inparallel with the longitudinal axis of the reflector trough.